Specifically, in order to constitute a fluid dispenser, it is necessary to mount the dispenser member (pump or valve) in stationary and leaktight manner on the neck of a reservoir that may be pre-filled with fluid. In general, the dispenser member is provided with a mounting ring that comes into stationary and leaktight engagement with the outside, or even the inside, of the neck of the reservoir. The most widespread fastener techniques for mounting the fastener ring on the neck of the reservoir are snap-fastening and screw-fastening, both requiring an axial mounting movement to be imparted downwards on the fastener ring.
It has been known for a long time to use a mounting head that is moved axially in order to impart the axial mounting movement to the dispenser member, and more particularly to its fastener ring, which movement brings it from an axial arrangement in which it is merely placed on the neck into a final mounted position on the neck. Specifically, before arriving at the mounting station equipped with the mounting head of the invention, the dispenser member is merely placed on the neck at a prior station. Naturally, it is desired to place the dispenser member in accurately axial manner on the neck, so that the mounting head can come into engagement correctly with the dispenser member in order to impart the axial mounting movement thereto. However, it can frequently happen that the dispenser member is placed in an offset manner, i.e. sloping relative to the vertical axis. It can also happen that the dispenser member is placed in axial or upright manner, but that it becomes offset or sloping while being transferred from the placing station to the mounting station. Under such circumstances, while the mounting head is being moved downwards, it cannot come into engagement correctly with the dispenser member, which may then be damaged or mounted in non-leaktight manner on the neck.
In the prior art, document EP 1 886 968 is known, which describes a mounting head for gripping a cap so as to make it possible to turn it in order to screw-fasten it on a threaded receptacle neck. The head forms arms that are constrained in their rest position by two outer resilient rings, such that the inside diameter of the arms is smaller than the outside diameter of the cap. Thus, the arms cannot perform a function of axial centering.